For those interested, the way to track down this bug is to start with the source for Ext.form.Basic, setValues method. Inside the setValues method there is a helper function setVal that looks like this:

This specialized setValue method takes into account that there are multiple radios with the same name, and that setValue is called on just one of them (the first one found by calling findField in basic form's setValues. So, setValue for radio field has been made "smart". Now, what about resetOriginalValue for the radio field? A specialized resetOriginalValue for radio fields was never implemented - it is simply inherited from the default in Ext.form.field.Field, which looks like this: